The theory that pigs can be used to grow human-compatible organs took a step closer to reality in October of 2002. In a study published in the Proceedings of the National Academy of Sciences, researchers from the University of Milan report they were able to develop a strain of swine that carried human genes in their hearts, livers, and kidneys. The scientists mixed human DNA with pig sperm; then, the manipulated sperm were used to fertilize pig eggs. Twenty litters of 205 piglets were produced using the new technique. Tests found human genes present in 20 to 50 percent of the piglets' central organs, and also that those human genes would be passed along to later generations. Pig parts have already been used to replace human heart valves, but pig organs with human genes are still not ready for actual transplants because of the complexity involved. There are other pig genes that need to be eradicated or replaced before the human immune system can accept the organs, and there are concerns about the possible transfer of unrecognized swine viruses. The Italian scientists are hopeful that they can develop and breed pigs with fully human-compatible organs within two years. More than 4,000 people die every year awaiting donor organs, and it's hoped that the use of pigs to grow transplantable organs will relieve the shortage.

– 6+ Years Later –

Scientists in South Korea have cloned a pig whose organs can be transplanted into humans. Lim Gio-Bin lead the project that resulted in the birth of the cloned piglet to a surrogate mother at the National Institution of Animal Science in Suwon, Gyeonggi Province on April 3, 2009. Four cloned mini-pigs were produced from about 100 surrogate pigs but only one male named Xeno survived. Stem cells from smaller-than-normal pigs were taken to clone these "mini-pigs" (full growth weigh of 80 kilograms) with modified genes. The piglets were designed to lack the "alpha-gal" gene that causes tissue reaction exhibited in immuno-rejection. Antibodies in human blood attack alpha 1, 3-galactose, or "alpha gal," thus making it impossible for human bodies to accept non-human transplants for a long period of time. By producing a pig without the "alpha-gal" gene, researchers hope to create organs that would be safely transferable to humans. "Through mating we will be able to produce many genetically modified mini-pigs whose organs are more suitable for xenotransplantation (transplantation between different species)," Lim said. "Xeno will help us accumulate technology and resources, which can be used to produce many mini-pigs of good quality."